Iaijutsu Master

Iaijutsu Masters are masters of elegance in combat. Their flexibility and fluidity in their form allows them to draw their weapon, strike with it, and then resheathe it in one blindingly fast, devastatingly powerful motion. Their mastery of their form is focused wholly on their first strike, not allowing their opponents to recover from it before causing complete devastation. 

Lightning Blade

Starting at 3rd level, you are never caught unawares. Your studied nature allows you to know when danger is coming. You can give yourself a bonus to your initiative rolls equal to your Intelligence modifier. In addition, you can't be surprised, except when incapacitated by something other than nonmagical sleep. 

Iaijutsu Strike

Starting at 3rd level, you are able to focus your first strike to its deadliest end. At the start of your first turn of each combat, your walking speed increases by 30. If you take the Attack action on that turn, you can use your Sneak Attack against that target even if you don't have advantage on the attack roll, but not if you have disadvantage on it. In addition, any hit you score against a creature that hasn’t taken a turn in the combat yet with a melee weapon attack is a critical hit.

In addition, you can use Dexterity instead of Strength for the attack and damage rolls of longswords, and you can use your Sneak Attack when wielding a longsword. 

Canny Defense

Starting at 9th level, your training has granted you the ability to evade your foe's attacks by analyzing their movements and adjusting your own to compensate for their strikes. While you are wearing no armor and not wielding a shield, your AC equals 10+ your Dexterity modifier + your Intelligence modifier. 

Master's Focus

At 13th level, you have practiced calming your mind so much that you can make minute adjustments to better your results, even when it involves skills you do not possess. When you roll an ability check and the roll on the d20 is 10 or lower, you can reroll that ability check. If you do so, you must use the new roll. 

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

One Strike, Two Cuts

Starting at 17th level, the fluidity of your attacks has allowed you to make two strikes in one. If you take the Attack action to make a melee weapon attack on a creature that hasn't taken a turn in combat yet, you can make one additional melee weapon attack as a part of that action.  This attack can benefit from your Sneak Attack even if you have already used it this turn.